DevTools: migrate sidebar pane's titleElement to use Toolbar.

Source/devtools/front_end/sources/uiList.css

Index: Source/devtools/front_end/sources/uiList.css
diff --git a/Source/devtools/front_end/sources/uiList.css b/Source/devtools/front_end/sources/uiList.css
index 8a7006f5e308173222293e8593a67a202765b8cf..90cecca1358240956c956a2b63d96070fb2df9bd 100644
--- a/Source/devtools/front_end/sources/uiList.css
+++ b/Source/devtools/front_end/sources/uiList.css
@@ -5,19 +5,23 @@
  */
 
 .list-item {
-    padding: 3px 8px 4px 18px;
+    padding: 3px 8px 4px 8px;
     position: relative;
     min-height: 18px;
     white-space: nowrap;
 }
 
-.list-item:nth-of-type(2n) {
-    background-color: rgb(234, 243, 255);
+.list-item:hover {
+    background-color: #eee;
 }
 
-.list-item.selected {
-    background-color: #cfcfcf;
-    background-clip: padding-box;
+.list-item > .title::before {
+    content: "\2713 ";
+    color: transparent;
+}
+
+.list-item.selected > .title::before {
+    color: inherit;
 }
 
 .list-item > .title {
@@ -26,6 +30,10 @@
     white-space: normal;
 }
 
+.list-item.selected > .title {
+    font-weight: bold;
+}
+
 .list-item > .subtitle {
     margin-left: 5px;
     color: rgba(0, 0, 0, 0.7);